[Jak0zilla]

Hi, I'm hoping someone else has already gone down this particular path before me and can share their experience. I'd like to use a set of non-MicroDrive Suntour XC Pro crankarms with a single chainring as a single speed crankset.

I know the original BB spindle for the triple setup was 125.5mm long, can anyone tell me what they've used on this crank (or perhaps on the similar Ritchey Logic or Sugino XP cranks) as a bottom bracket to give a good chainline. I was thinking I'd use the middle position for my chainring, the outer for a guard, and leave off the inner.

Apologies in advance if I've missed the answer in the archives, but I couldn't seem to turn anything up with my searches.

 

[girlonbike]

A. You don't. You get a Sugino Messenger. HAHAHAHA! :band:

JK, Jack! You probably didn't come up with anything in your search cuz this ain't the singlespeed forum. haha! Okay, okay. Good thing we know each other...even though we've never met!

I'll give you the depends on your bike chainstay answer.

 

[misterdangerpants]

Don't know if this will help but I currently run a Kooka compact crankset with a single chainring (36T) and use a 113mm bottom bracket.

 

[Jak0zilla]

JK, Jack! You probably didn't come up with anything in your search cuz this ain't the singlespeed forum. haha! Okay, okay. Good thing we know each other...even though we've never met!

Ehh ... but they only talk about this year's model 29'ers blah blah blah. I'm trying to SS a 1992 Bontrager with vintage parts. They'd just laugh at me for my cranky old man bike, and tell me to buy a plastic bike with 36" wheels.

 

[jeff]

I ran a set of 170's on a modern 29"er with curvy stays. I was able to get away with a 110ish XC pro bb. Set up as a triple the same set of cranks on my Bonty CX took a 118.

 

[Jak0zilla]

Thanks Jeff, I suppose I should just start plugging in the BB's I have and see how it works out. Was that set on your 29'er run as a single?

I suppose it may end up being a set of those Suginos that Girlonbike recommended in the end. They're not vintage, but a least they don't look like they were designed by the team at Hasbro responsible for the the Big Wheel tricycle like most modern cranksets do IMHO.

 

[Shayne]

If you're going to use the middle ring position you should just stick with the stock BB length. That will give you a chainline centered on the freehub.
If you're going with a SS specific rear wheel, measure where the cog falls on the axle and adjust the spindle length accordingly.

 

[jeff]

Thanks Jeff, I suppose I should just start plugging in the BB's I have and see how it works out. Was that set on your 29'er run as a single?

I suppose it may end up being a set of those Suginos that Girlonbike recommended in the end. They're not vintage, but a least they don't look like they were designed by the team at Hasbro responsible for the the Big Wheel tricycle like most modern cranksets do IMHO.

Yep. Set up as a single. Middle position with the shortest possible spindle length for Q factor. I used a cassette hub with spacers for chain line.

 

[N10S]

It all depends on your crankset. If you are using the original crank that you used with the 125.5mm bb, then you will end up having to use the same wider spindled bottom bracket. Older vintage cranks like the 730 XT or suntour XC are not low profile like a 737 XT or Race Face LP which are designed around a narrower 110-113mm bb. I will have my 91 OR next week and am thinking about using my rf lp crankset with my 113mm bb, and will let you know how it goes. Single ring or triple though, its really relative to the cranks and not the number of rings.

 

[DeeEight]

Yes and since when running a triple-crank as a single you almost ALWAYS use the middle ring position, and the proper chainline BB size is always based on the middle ring position with triple cranks, the length doesn't change at all by eliminating two chainrings.